The field of this invention is underwater diving, and in particular apparatus substantially contributing to the successful and safe recovery of expired diving gas.
In underwater diving situations, and in particular in deep sea diving situations, where the diver must be underwater for extended periods, it is known to provide a breathing gas at a pressure at least slightly greater than the hydrostatic pressure of the water environment in which the diver is operating. Normal air containing nitrogen cannot be used safely as a breathing gas because nitrogen tends to become absorbed in the blood and tissues of the diver. Absorbed nitrogen must be removed before the diver is exposed to ambient air pressures or the absorbed nitrogen will expand within the blood and tissues and possibly kill the diver. This phenomenon is generally known as nitrogen narcosis. Because nitrogen is unsafe, helium has been effectively substituted for nitrogen. Helium is extremely inert and is not absorbed by the body. However, helium is a rare gas and is therefore extremely expensive to produce in sufficient quantities to use during extended diving operations. Helium is used most often in a mixture with oxygen only. Sometimes a small percentage of nitrogen is included in the helium-oxygen mixture to enhance sound transfer. Another mixture sometimes used is a hydrogen-oxygen mixture. The disadvantage of a hydrogen-oxygen mixture is the explosiveness of hydrogen. So a helium-oxygen mixture, with perhaps some nitrogen, is the most desirable breathing gas presently used.
Until a few years ago, the helium-oxygen mixture breathed by a diver was continuously delivered to the diver's helmet and simply exhausted from the diver's helmet to the water environment. Simple exhaustion of the helium-oxygen mixture constitutes a total waste of the helium, which is certainly costly. A partial solution to this expensive waste of helium has been found in a diver carried scrubber that circulates expired breathing gas through a carbon dioxide scrubber and back into the helmet or other breathing habitat. Since no oxygen is added, the gas must be expelled to the water environment when the oxygen is spent.
In more recent years, there have been several patents issued disclosing reconditioning systems for receiving the expired breathing gas from the diver's helmet and effectively reconditioning the breathing gas for reuse. For example, U.S. Pat. No. 3,802,427 (and divisional Pat. Nos. 3,924,618; 3,924,616 and 3,924,619) disclose a method and apparatus for reconditioning the expired breathing gas of a diver. The reconditioning process disclosed in these patents, all owned by Taylor Diving & Salvage Co., Inc., includes a carbon dioxide scrubber, a water removal means and an oxygen additive device for making up for oxygen expended through the breathing process. After the expired breathing gas is reconditioned, it is then delivered again to the diver's helmet. The helmet disclosed in the Taylor Diving patents includes an incoming line for delivering breathable gas and a recovery line for returning expired breathing gas to the reconditioning system, which may be located on the surface or in a subsurface module. The incoming line includes a check valve and a throttle valve for controlling the flow of breathable gas into the helmet. The recovery line includes a safety shut-off valve and a back pressure regulator valve to control the pressure in the recovery line.
U.S. Pat. No. 3,831,594 of Charles R. Rein also discloses a system for reconditioning expired breathing gas and delivering the expired breathing gas back to the diver's mouth piece or habitat at operating depth. The basic steps of the Rein patent involved in reconditioning the expired breathing gas are similar to those of the Taylor Diving patents except that cryogenic means are used to refresh the oxygen supply. No particular helmet is disclosed in this patent. However, a schematic discloses the connection of a check valve to the incoming line to be connected to the habitat, which may, of course, be a diving helmet, and another check valve to be mounted in the recovery line which takes expired breathing gas away from the habitat. Another process for reconditioning spent breathing gas is disclosed in U.S. Pat. No. 3,941,124 of Rodewald, et al. Again, no particular helmet structure is disclosed in the Rodewald patent. U.S. Pat. No. 3,859,994 of Almqvist, et al. Also discloses a exhaled gas reconditioning system, without disclosing a particular helmet structure. The Almqvist patent does refer to the mounting of a pressure regulator in the helmet recovery line to evidently control the pressure therein. U.S. Pat. No. 3,481,333 of Garrison may also be of interest.
At this point, it is reasonable to conclude that there is probably more than one diving gas recovery system available which can effectively recondition the exhaled breathing gas of the diver by the suitable removal of carbon dioxide and water and addition of oxygen in order to continuously reuse that valuable commodity--helium. Concerning the helmets, several of the patents disclose the use of check valves and/or regulator valves in the incoming and outgoing lines from a diver's helmet or other habitat. However, none of these patents discussed refer to any particular problems with the helmet.
It is known that the breathing gas supplied to the helmet must be delivered at a pressure higher than the hydrostatic pressure of the depth at which the helmet is being used. Thus, the spent or expired breathing gas delivered to the recovery line connected to the helmet is also at a higher pressure than the hydrostatic pressure of the water environment at the depth of use of the helmet. But, this is only the normal situation. It has been discovered that the pressures in the recovery line may be dangerously unpredictable and can actually reach such low levels that a dangerous suction or negative pressure is created in the recovery line. This undesirable suction may be deadly to the diver, for it may draw out all the breathing air out of the diver's helmet. The mounting of check valves such as disclosed in U.S. Pat. Nos. 3,802,427 and 3,831,594 and pressure regulators such as disclosed in U.S. Pat. No. 3,859,994 in the recovery lines may be attempts to prevent a dangerous change in pressure from being applied to the interior of the helmet. Unfortunately, the use of such valves has not been successful in all situations. For valves have moving parts and moving parts are subject to failure under stress, which may result in the death of a diver.